Environmental measurement apparatus and environmental measurement method

ABSTRACT

An environmental measurement apparatus includes an operation unit which calculates a first change in a first oscillation frequency of a first QCM sensor and a second change in a second oscillation frequency of a second QCM sensor. The operation unit corrects the second change based on the first change in a first period and the second change in the first period.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of InternationalApplication PCT/JP2012/65023 filed on Jun. 12, 2012 and designated theU.S., the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to an environmentalmeasurement apparatus and an environmental measurement method.

BACKGROUND

In some cases, the atmosphere contains corrosive gases that corrodeelectronic devices. The emission sources of the corrosive gases includea chemical plant such as a paper mill and a rubber factory, a wastetreatment plant, a sewage treatment plant, a volcano, commoditiescontaining chemicals, and the like.

One of the corrosive gases emitted from such emission sources ishydrogen sulfide gas. The hydrogen sulfide gas can corrode wires in anelectronic device and break the electronic device. Particularly, in thecase where an information society uses electronic devices to support thefoundation of the system in social infrastructure, breakdown of theelectronic devices may paralyze social activities.

In order to prevent breakdown of electronic devices due to the corrosivegas, it is useful to monitor the corrosive gas contained in anenvironment where the electronic devices are installed and to know inadvance a possibility of the electronic devices breaking down due tocorrosion caused by the corrosive gas.

A QCM (Quartz Crystal Microbalance) sensor is known as a sensor tomonitor the corrosive gas. The QCM sensor is a mass sensor capable ofmeasuring a minute change in mass by using a property that, when themass of electrodes on a crystal oscillator is changed by corrosion, thecrystal oscillator reduces its oscillation frequency according to theamount of the corrosion.

In the QCM sensor, a change in the oscillation frequency grows as theamount of corrosion is increased over time, and the QCM sensor comes tothe end of its life. For this reason, in the case of monitoring thecorrosive gas over a long time period, it is preferable that a QCMsensor whose life is close to the end be replaced with a new QCM sensorto prevent a blank period in monitoring.

However, since QCM sensors have individual differences, the replaced QCMsensor cannot necessarily maintain the measurement accuracy for theamount of corrosion caused by the corrosive gas.

SUMMARY

According to one aspect of the following disclosure, there is providedan environmental measurement apparatus including an operation unit whichcalculates a first change in a first oscillation frequency of a firstQCM sensor and a second change in a second oscillation frequency of asecond QCM sensor, wherein the operation unit corrects the second changebased on the first change in a first period and the second change in thefirst period.

According to another aspect of the following disclosure, there isprovided an environmental measurement method, the method includingcalculating a first change in a first oscillation frequency of a firstQCM sensor; calculating a second change in a second oscillationfrequency of a second QCM sensor; and correcting the second change basedon the first change in a first period and the second change in the firstperiod.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a QCM sensor used in an examination;

FIGS. 2A and 2B are graphs obtained by examining individual variationsof the QCM sensors;

FIG. 3 is a configuration diagram of an environmental measurementapparatus according to a first embodiment;

FIG. 4 is a circuit diagram of an oscillation circuit included in theenvironmental measurement apparatus according to the first embodiment;

FIG. 5 is an enlarged view around connectors in a drive unit included inthe environmental measurement apparatus according to the firstembodiment;

FIG. 6 is a graph illustrating an example of a result of measurementusing QCM sensors included in the environmental measurement apparatusaccording to the first embodiment;

FIG. 7 is a flowchart for explaining an environmental measurement methodaccording to the first embodiment;

FIG. 8 is a diagram for explaining a method for calculating a firstcorrection coefficient in the first embodiment;

FIG. 9 is a diagram illustrating a second graph after correction in thefirst embodiment;

FIG. 10 is a perspective view of a sensor unit used in a secondembodiment;

FIG. 11 is a development diagram of a shutter included in the sensorunit used in the second embodiment;

FIG. 12 is a cross-sectional view taken along the line I-I in FIG. 10;

FIG. 13 is a configuration diagram of an environmental measurementapparatus according to the second embodiment;

FIGS. 14A to 14C are plan views for explaining operations of the sensorunit used in the second embodiment;

FIG. 15 is a plan view of a sensor unit used in a third embodiment;

FIG. 16A is a plan view of a first rotating plate used in the thirdembodiment, and FIG. 16B is a plan view of a second rotating plate 52used in the third embodiment;

FIG. 17A is a cross-sectional view taken along the line II-II in FIG.15, and FIG. 17B is an enlarged cross-sectional view when a desiccant ishoused in the second rotating plate;

FIG. 18 is an enlarged cross-sectional view of an opening edge of ahousing in the sensor unit according to the third embodiment;

FIG. 19 is a configuration diagram of an environmental measurementapparatus according to the third embodiment;

FIGS. 20A to 20C are diagrams illustrating states of the sensor unit ata time before a first time in the third embodiment;

FIGS. 21A to 21C are diagrams illustrating states of the sensor unit ata time between the first time and a second time in the third embodiment;

FIGS. 22A to 22C are diagrams illustrating states of the sensor unit ata time after the second time in the third embodiment;

FIG. 23 is a plan view of a QCM sensor according to a fourth embodiment;

FIG. 24 is a configuration diagram of an environmental measurementapparatus according to a fifth embodiment;

FIG. 25 is a perspective view of a sensor unit used in the fifthembodiment;

FIG. 26 is a cross-sectional view taken along the line III-III in FIG.25;

FIG. 27 is an enlarged view of a second QCM sensor and a drive unit inthe fifth embodiment;

FIG. 28 is a graph illustrating an example of a result of measurementusing QCM sensors according to the fifth embodiment;

FIG. 29 is a flowchart for explaining an environmental measurementmethod according to the fifth embodiment;

FIG. 30 is a diagram for explaining a method for calculating a firstcorrection coefficient in the fifth embodiment;

FIG. 31 is a graph obtained from measurement values generated in thefifth embodiment;

FIG. 32 is an enlarged view of the graph in FIG. 31;

FIG. 33 is a plan view of a sensor unit used in a sixth embodiment;

FIG. 34 is a plan view of a shutter included in the sensor unit used inthe sixth embodiment;

FIG. 35 is a cross-sectional view taken along the line IV-IV in FIG. 33;

FIG. 36 is a configuration diagram of an environmental measurementapparatus according to the sixth embodiment;

FIGS. 37A to 37D are plan views for explaining operations of the sensorunit included in the environmental measurement apparatus according tothe sixth embodiment;

FIG. 38A is a plan view of a sensor unit used in a seventh embodiment,and FIG. 38B is a cross-sectional view taken along the line V-V in FIG.38A;

FIG. 39 is a development diagram of a shutter included in the sensorunit used in the seventh embodiment;

FIG. 40 is a configuration diagram of an environmental measurementapparatus according to the seventh embodiment;

FIGS. 41A to 41E are plan views for explaining operations of the sensorunit included in the environmental measurement apparatus according tothe seventh embodiment; and

FIG. 42 is a graph illustrating an example of a result of measurementusing QCM sensors used in an eighth embodiment.

DESCRIPTION OF EMBODIMENTS

Prior to description of embodiments, the result of examination conductedby the inventor of the present application is described. In thisexamination, the individual differences between QCM sensors are examinedas follows.

FIG. 1 is a perspective view of a QCM sensor 1 used in the examination.

The QCM sensor 1 includes a disk-shaped crystal oscillator 5, a firstelectrode 6 formed on one main surface of the crystal oscillator 5, anda second electrode 7 formed on the other main surface of the crystaloscillator 5.

The size and cut of the crystal oscillator 5 are not particularlylimited. In this examination, an AT-cut crystal oscillator 5 of 8 mm indiameter is used.

Also, the materials of the first and second electrodes 6 and 7 areselected according to a corrosive gas to be detected. For example, inthe case of detecting hydrogen sulfide, silver can be used as thematerial of the first and second electrodes 6 and 7. Alternatively, inthe case of detecting chlorine, copper can be used as the material ofthe first and second electrodes 6 and 7.

Moreover, conductive wires 8 made of gold or the like are electricallyconnected to the first and second electrodes 6 and 7 through lead wires9, respectively. The crystal oscillator 5 is supported by the conductivewires 8.

In actual use, the crystal oscillator 5 is oscillated by applying apredetermined voltage between the first and second electrodes 6 and 7through the conductive wires 8. The crystal oscillator 5 is oscillatedat a oscillation frequency called a fundamental frequency F at the startof its use. However, as the mass of the first and second electrodes 6and 7 increases due to corrosion, the oscillation frequency f isgradually decreased.

Here, a change Δf_(m) (=F−f) in the frequency f when the total mass ofthe first and second electrodes 6 and 7 is increased by M_(f) comparedwith the start of the use is expressed by the following Sauerbreyequation (1).

$\begin{matrix}{{\Delta\; f_{m}} = {{- \frac{2\; F^{2}}{\sqrt{\rho_{q}\mu_{q}}}}\frac{M_{f}}{S}}} & (1)\end{matrix}$

Here, F denotes fundamental oscillation frequency, ρ_(q) denotes densityof quartz, ρ_(q) is shear stress of quartz, and S is total surface areaof the first and second electrodes 6 and 7.

In the early period of measuring an amount of corrosion caused by thecorrosive gas using the QCM sensor 1, corrosion of the first and secondelectrodes 6 and 7 progresses according to the concentration of thecorrosive gas in the environment. Therefore, in this period, a timechange occurring in the increase M_(f) of the mass can be read with goodsensitivity as Δf_(m) by the Sauerbrey equation (1).

However, when the corrosion reaches large portions of the first andsecond electrodes 6 and 7, the corrosion of the electrodes slows downand eventually goes into saturation. Therefore, Δf_(m) can no longer beread from the mass increase M_(f). Moreover, even before the corrosionstops, a load on the oscillation of the crystal oscillator 5 isincreased too much by the increase of mass of the first and secondelectrodes 6 and 7 due to the corrosion. As a result, the oscillationfrequency may exceed a stable oscillation range and become unstable. Insuch a case, the corrosive gas cannot be monitored any more with the QCMsensor 1, and the QCM sensor 1 comes to the end of its life.

When the QCM sensor comes to the end of its life in this manner, the oldQCM sensor is replaced with a new QCM sensor in order to continuelong-term monitoring of the amount of corrosion caused by the corrosivegas. In this event, when the old and new QCM sensors have differentspecifications, the proportionality constant (−2F²/(ρ_(q)μ_(q))^(1/2))on the right-hand side of Equation (1) changes from the one before thereplacement. This makes it impossible to grasp variations in the amountof corrosion caused by the corrosive gas before and after thereplacement. As a result, the accuracy of measurement of the amount ofcorrosion caused by the corrosive gas is reduced.

Therefore, when replacing the old QCM sensor with a new one, it ispreferable to replace the QCM sensor with one having the samespecifications as those of the old one. Here, the specifications of theQCM sensor include the size and pane of the crystal oscillator 5, thesize and material of each of the first and second electrodes 6 and 7,and the like, for example.

However, despite the attempt to use the QCM sensors with the samespecifications, variations in material and processing at the time ofmanufacture actually cause the proportionality constant on theright-hand side of Equation (1) to take values that vary from one QCMsensor to another. Moreover, the way the electrodes are corroded alsovaries from one QCM sensor to another. This leads to individualdifference in corrosion characteristics of the QCM sensors.

FIGS. 2A and 2B are graphs obtained by examining such individualdifferences.

FIG. 2A illustrates the result obtained by using silver as the materialof the first and second electrodes 6 and 7 and exposing the QCM sensor 1to an atmosphere containing hydrogen sulfide. Note that the temperatureof the atmosphere is 25° C. and the relative humidity thereof is 50%.Also, the concentration of the hydrogen sulfide in the atmosphere is0.25 ppm.

In FIG. 2A, the horizontal axis represents exposure time of the QCMsensor 1 to the atmosphere described above, while the vertical axisrepresents the change Δf_(m) in the oscillation frequency.

Although FIG. 2A illustrates a plurality of graphs, these graphs areobtained by using QCM sensors having the same specifications within thesame lot.

The graphs do not completely overlap with each other, and the change inoscillation frequency varies by up to about 10% between the graphs. Inthe case of QCM sensors from different lots, graphs are expected to varymore than those illustrated in FIG. 2A.

Thus, it was confirmed that QCM sensors show individual differences evenif they have the same specification.

FIG. 2B is a graph obtained by using a metal layer having a two-layerstructure as each of the first and second electrodes 6 and 7 andconducting the same examination as that illustrated in FIG. 2A. Notethat a gold layer that serves to electrically connect each of theelectrodes 6 and 7 to the wire 8 is formed as a lowermost layer of themetal layer having the two-layer structure, and a copper layer is formedas metal to be corroded in an uppermost layer.

Note that when the first and second electrodes 6 and 7 are formed tohave a multi-layer structure in this manner, a metal layer may be formedbetween layers to increase adhesion between the layers. Moreover, ametal layer may be formed between the first electrode 6 and the crystaloscillator 5 to increase their adhesion strength. Furthermore, a metallayer may be formed between the second electrode 7 and the crystaloscillator 5 to increase their adhesion strength.

In this case, again, it was found out that the QCM sensors showindividual difference as in the case of FIG. 2A.

Such individual difference causes a difference in tendency of measuredvalues between the old QCM sensor that has reached the end of its lifeand the new QCM sensor after replacement. This makes it difficult tomonitor with high accuracy the amount of corrosion caused by thecorrosive gas in the atmosphere over a long time.

In order to predict the individual differences of the QCM sensors, it isalso conceivable to create graphs as illustrated in FIGS. 2A and 2B byactually corroding the QCM sensors in the early stage of themeasurement. However, this method does not necessarily allow thecorrosion to progress as expected, and ends up shortening the life ofthe QCM sensor by the amount of corrosion.

In the following, the embodiments are described.

First Embodiment

In this embodiment, a corrosive gas is monitored over a long time byreplacing the old QCM sensor with the new QCM sensor. Moreover, themeasurement accuracy of the amount of corrosion caused by the corrosivegas is maintained by taking into consideration the individual differenceof the old and new QCM sensors during replacement.

FIG. 3 is a configuration diagram of an environmental measurementapparatus according to this embodiment.

The environmental measurement apparatus 10 includes a drive unit 13 andan operation unit 14.

The drive unit 13 is connected to an old first QCM sensor 11 a beforereplacement and a new second QCM sensor 11 b after replacement.

Note that the first and second QCM sensors 11 a and 11 b have the samestructure as that illustrated in FIG. 1 and have the samespecifications. In this embodiment, a crystal oscillator 5 in each ofthe first and second QCM sensors 11 a and 11 b is 8 mm in diameter, anda silver film having a thickness of 0.1 μm is formed as each ofelectrodes 6 and 7. Also, the fundamental oscillation frequency of thefirst and second QCM sensors 11 a and 11 b is 25 MHz, for example.

Furthermore, aging treatment may be performed to corrode the electrodes6 and 7 in the first and second QCM sensors 11 a and 11 b to some extentin advance. The aging treatment enables measurement within a more stablecorrosion characteristic range while avoiding a sudden change incorrosion characteristics in the early stage of the measurement asillustrated in FIGS. 2A and 2B. This is also the case for theembodiments to be described later.

The drive unit 13 includes first and second oscillation circuits 16 aand 16 b and first and second frequency counters 18 a and 18 b.

The first and second oscillation circuits 16 a and 16 b are circuits tooscillate the first and second QCM sensors 11 a and 11 b, respectively,at their fundamental oscillation frequency.

FIG. 4 is a circuit diagram of the first oscillation circuit 16 a. Notethat a circuit diagram of the second oscillation circuit 16 b is thesame as that illustrated in FIG. 4, and thus description thereof isomitted here.

As illustrated in FIG. 4, the first oscillation circuit 16 a includes aninverter 17, first and second resistors R1 and R2, and first and secondcapacitors C1 and C2. By properly setting values thereof, the first QCMsensor 11 a can be stably oscillated at a predetermined oscillationfrequency.

In such a circuit, the inverter 17 forms a parallel oscillation circuitwith the first QCM sensor 11 a, and the first QCM sensor 11 a can beoscillated by appropriately setting capacitance values of the first andsecond capacitors C1 and C2.

Note that the magnitude of crystal current flowing through the first QCMsensor 11 a is adjusted by the first resistor R1. A power-supply voltageVdd is applied to the inverter 17, and the second resistor R2 functionsas a feedback resistor of the inverter 17.

FIG. 3 is referred to again.

The first frequency counter 18 a is connected to the first oscillationcircuit 16 a to measure a first oscillation frequency f_(1m) of thefirst QCM sensor 11 a. Likewise, the second frequency counter 18 b isconnected to the second oscillation circuit 16 b to measure a secondoscillation frequency f_(2m) of the second QCM sensor 11 b.

The operation unit 14 is a computer such as a personal computer, andacquires the first oscillation frequency f_(1m) and the secondoscillation frequency f_(2m) from the drive unit 13.

FIG. 5 is an enlarged view around connectors in the drive unit 13.

As illustrated in FIG. 5, the drive unit 13 is provided with fourconnectors 19, to and from which the conductive wires 8 in the first andsecond QCM sensors 11 a and 11 b can be attached and detached.

In this embodiment, a user firstly inserts the first QCM sensor 11 ainto the connectors 19 and monitors the amount of corrosion caused bythe corrosive gas in the atmosphere with the first QCM sensor 11 a.Then, as the life of the first QCM sensor 11 a approaches its end, theuser attaches the new second QCM sensor 11 b to the connectors 19.

FIG. 6 is a graph illustrating an example of a result of measurementusing the first and second QCM sensors 11 a and 11 b.

Note that the horizontal axis of FIG. 6 represents time that has elapsedsince the start of measurement with the first QCM sensor 11 a. Also, thevertical axis of FIG. 6 represents a first change Δf_(1m) in the firstoscillation frequency f_(1m) of the first QCM sensor 11 a and a secondchange Δf_(2m) in the second oscillation frequency f_(2m) of the secondQCM sensor 11 b.

Let F₁ and F₂ be the fundamental frequencies of the first and second QCMsensors 11 a and 11 b respectively. Then, the changes Δf_(1m) andΔf_(2m) are defined as Δf_(1m)=F₁−f_(1m) and Δf_(2m)=F₂−f_(2m)respectively.

Also, in FIG. 6, the first change Δf_(1m) is represented by a firstgraph A₁ and the second change Δf_(2m) is represented by a second graphA₂.

In this embodiment, as illustrated in FIG. 6, a first period T₁ isprovided, during which the measurement is conducted with both of thefirst and second QCM sensors 11 a and 11 b.

A first time t_(s), which is the beginning of the first period T₁, isthe time when the first change Δf_(1m) in the oscillation frequency ofthe first QCM sensor 11 a reaches a predetermined first specified valueF_(sm).

A second time t_(c), which is the end of the first period T₁, is thetime when the first change Δf_(1m) reaches a predetermined secondspecified value F_(cm).

As to the specified values, the second specified value F_(cm) is thefirst change Δf_(1m) at which the first QCM sensor 11 a is determined tohave reached the end of its life. Meanwhile, the first specified valueF_(sm) is the first change Δf_(1m) at which the first QCM sensor 11 a isdetermined to be close to the end of its life.

A method for setting the first specified value F_(sm) is notparticularly limited. For example, another QCM sensor having the samespecifications as those of the first QCM sensor 11 a is actuallycorroded, and a change in oscillation frequency when the QCM sensorcomes to the end of its life is measured. Then, a value smaller by about1 to 5% than the change can be set as the first specified value F_(sm).Moreover, in this embodiment, correction is performed using the changesΔf_(1m) and Δf_(2m) in the first period T₁, as described later.Therefore, the longer the first period T₁, the more data needed for thecorrection can be collected.

Note that, taking the individual differences in the specification of theQCM sensors into consideration, it is preferable that the specifiedvalue F_(cm) is set in anticipation of a certain amount of margin. Byincreasing the margin in this manner, more reliable and accuratecorrection can be performed. However, in order to prevent reduction in aperiod during which measurement can be performed before replacement ofthe QCM sensor, i.e., the substantial life, it is preferable that thespecified value F_(cm) is set to an appropriate value in considerationof the purpose of measurement and the like.

During the first period T₁, the corrosive gas in the same atmosphere ismonitored using the first and second QCM sensors 11 a and 11 b havingthe same specifications. Therefore, corrosion rates obtained fromresults of measurement using the first and second QCM sensors 11 a and11 b, i.e., rates of changes in frequency, are expected to be the same.

However, variations in the measurement results due to the individualdifference as described above cause a difference in the slope of thegraph (corrosion rate) during the first period T₁ between the first andsecond QCM sensors 11 a and 11 b as illustrated in FIG. 6.

To deal with this problem, in this embodiment, the slope of the secondgraph A₂ is matched with the slope of the first graph A₁ by correctingthe second change Δf_(2m) of the second QCM sensor 11 b as follows.

FIG. 7 is a flowchart for explaining an environmental measurement methodaccording to this embodiment.

In the first Step S1, the operation unit 14 acquires the firstoscillation frequency f_(1m) of the first QCM sensor 11 a at a time t,and calculates the first change Δf_(1m) in the oscillation frequencyf_(1m) at the time t. The first change Δf_(1m) is a difference(F₁−f_(1m)) between the fundamental frequency F₁ which is theoscillation frequency of the first QCM sensor 11 a at time 0 and thefirst oscillation frequency f_(1m) at the time t.

Next, in Step S2, the operation unit 14 determines whether or not thefirst change Δf_(1m) is equal to or more than the first specified valueF_(sm).

Here, when it is determined that the first change Δf_(1m) is not equalto or more than the first specified value F_(sm) (NO), the first QCMsensor 11 a is considered to be not close to the end of its life yet.Thus, the processing returns to Step S1 to continue the measurementusing the first QCM sensor 11 a.

On the other hand, when it is determined in Step S2 that the firstchange Δf_(1m) is equal to or more than the first specified value F_(sm)(YES), the time t is within the aforementioned first period T₁. Thus, itis considered that the life of the first QCM sensor 11 a is coming closeto the end.

Therefore, in this case, the processing moves to Step S3, where the userattaches the new second QCM sensor 11 b to the drive unit 13 to preparefor measurement using the second QCM sensor 11 b.

Next, in Step S4, the operation unit 14 starts acquiring the secondoscillation frequency f_(2m) of the second QCM sensor 11 b. Consideringthe labor for attaching the second QCM sensor 11 b or the like, thestart time is slightly behind the first time t_(s) about a few secondsto a few minutes. However, the second oscillation frequency f_(2m) issubstantially started to be acquired at the first time t_(s).

Then, the operation unit 14 starts calculating the second change Δf_(2m)in the second oscillation frequency f_(2m) at the time t. The secondchange Δf_(2m) is a difference (F₂−f_(2m)) between the fundamentalfrequency F₂ which is the oscillation frequency of the second QCM sensor11 b at the first time t_(s) and the second oscillation frequency f_(2m)at the time t.

Next, in Step S5, the operation unit 14 determines whether or not thefirst change Δf_(1m) is equal to or more than the second specified valueF_(cm).

Here, when it is determined that the first change Δf_(1m) is not equalto or more than the second specified value F_(cm) (NO), it is consideredthat the life of the first QCM sensor 11 a is approaching the end butdoes not yet reach the end. Thus, the processing returns to Step S4.

On the other hand, when it is determined in Step S5 that the firstchange Δf_(1m) is equal to or more than the second specified valueF_(cm) (YES), it is considered that the first QCM sensor 11 a come tothe end of its life.

Thus, in this case, the processing moves to Step S6 to end theacquisition of the first oscillation frequency f_(1m) with the first QCMsensor 11 a. The end time is the second time t_(c) when the first changeΔf_(1m) becomes equal to the second specified value F_(cm).

Then, in Step S7, the operation unit 14 calculates the second changeΔf_(2m) at the second time t_(c). Hereinafter, the second change Δf_(2m)thus calculated is described as F_(em) in this embodiment. F_(em)corresponds to an increment of the second change Δf_(2m) within thefirst period T1, and is an example of a second increment.

Thereafter, in Step S8, the operation unit 14 calculates a firstcorrection coefficient C₁ to correct the second change Δf_(2m) at andafter the first time t_(s).

FIG. 8 is a diagram for explaining a method for calculating the firstcorrection coefficient C₁. In FIG. 8, the graph A₂ illustrated in FIG. 6is translated in the vertical axis direction to match the starting pointof the graph A₂ with the graph A₁ at the first time t_(s).

Due to a difference in slope between the graphs A₁ and A₂, the graphs A₁and A₂ cannot be connected by simply translating the graph in thevertical axis direction.

In this step, in order to resolve such a difference in slope, theoperation unit 14 calculates the first correction coefficient C₁ bywhich the second change Δf_(2m) is to be multiplied as follows.

First, a first increment F_(em)−F_(sm) of the first change Δf_(1m)within the first period T₁ is calculated.

Next, a first ratio (F_(em)−F_(sm))/F_(em) of the first incrementF_(em)−F_(sm) to the second increment F_(em) is calculated, and thefirst ratio is set as the first correction coefficient C₁. The firstcorrection coefficient C₁ thus calculated is equal to a ratio betweenthe slopes of the graphs A₁ and A₂ in FIG. 6 during the period T₁.

Then, in Step S9, the operation unit 14 corrects the second changeΔf_(2m) by multiplying the second change Δf_(2m) at and after the firsttime t_(s) by the first correction coefficient C₁.

As described above, the first correction coefficient C₁ is equal to theratio between the slopes of the graphs A₁ and A₂. Therefore, bymultiplying the second change Δf_(2m) by the first correctioncoefficient C₁ in this step, the graph A₂ can be corrected to match theslope thereof with the slope of the graph A₁.

However, only the slopes of the graphs A₁ and A₂ are matched in thisstep, and heights of the graphs are not matched.

Therefore, in Step S10, the second change Δf_(2m) is corrected again byfurther adding the first specified value F_(sm), which is the firstchange Δf_(1m) at the first time t_(s), to the correction value(C₁×Δf_(2m)) calculated in Step S9.

FIG. 9 is a diagram illustrating the second graph A₂ after thecorrection.

As illustrated in FIG. 9, due to the correction made in Step S9, theslope of the graph A₂ in the first period T₁ coincides with the slope ofthe graph A₁. Moreover, the heights of the graphs A₁ and A₂ are matchedby the correction made in Step S10.

Thus, the basic steps of the environmental measurement method accordingto this embodiment are completed.

According to this embodiment described above, as illustrated in FIG. 9,the corrosive gas in the atmosphere can be monitored over a long time byusing the first and second QCM sensors 11 a and 11 b.

Moreover, by correcting the second change Δf_(2m) of the second QCMsensor 11 b, it can be prevented that the measurement result becomesinaccurate due to the individual difference between the first and secondQCM sensors 11 a and 11 b. Thus, the corrosive gas can be accuratelymonitored over the long time.

Second Embodiment

In the first embodiment, the QCM sensor, whose life is about to end, isreplaced with a new one by user's own hand. In this embodiment, the QCMsensor is automatically replaced as follows.

FIG. 10 is a perspective view of a sensor unit used in this embodiment.

The sensor unit 25 includes a housing 26 and a film-like shutter 28.

An opening 26 a is provided in the housing 26, and a first QCM sensor 11a and a second QCM sensor 11 b are housed in the opening 26 a. Althoughthe material of the housing 26 is not particularly limited, resin ormetal is used as the material thereof in this embodiment.

The shutter 28 can be moved in a longitudinal direction thereof by amotor 27, and has a window 28 a which overlaps with the opening 26 a.

FIG. 11 is a development diagram of the shutter 28.

The shutter 28 is formed by processing a flexible film such as a resinfilm, and the window 28 a has a rectangular shape in a planar view.Moreover, a portion of the shutter 28, in which the window 28 a is notformed, is used as a shield portion 28 b to cover the opening 26 a.

FIG. 12 is a cross-sectional view taken along the line I-I in FIG. 10.

As illustrated in FIG. 12, the shutter 28 is wound around two rollers 30in the housing 26, and the tension of the shutter 28 is adjusted byauxiliary rollers 31.

Also, a partition plate 32 is provided in the housing 26. The partitionplate 32 is a resin plate or metal plate, and separates a space in thehousing 26 into a first room 35 and a second room 36.

FIG. 13 is a configuration diagram of an environmental measurementapparatus 40 including the sensor unit 25. Note that, in FIG. 13, thesame components as those described in the first embodiment are denotedby the same reference numerals as those in the first embodiment, anddescription thereof is omitted below.

As illustrated in FIG. 13, a first QCM sensor 11 a and a second QCMsensor 11 b in the sensor unit 25 are connected to a drive unit 13.

Also, a control unit 15 to control a rotation amount of the motor 27 inthe sensor unit 25 is provided at the subsequent stage of an operationunit 14. In this embodiment, a computer such as a personal computer isused as the control unit 15.

Next, operations of the sensor unit 25 are described.

FIGS. 14A to 14C are plan views for explaining the operations of thesensor unit 25.

FIG. 14A illustrates a state where a time t is before a first timet_(s). At this time, as described in the first embodiment, the first QCMsensor 11 a is not close to the end of its life yet, and the amount ofcorrosion caused by a corrosive gas is measured by using only the firstQCM sensor 11 a.

Therefore, at this time, the first QCM sensor 11 a is exposed to theatmosphere containing the corrosive gas by communicating the window 28 aof the shutter 28 with the first room 35. Moreover, in order to preventcorrosion of electrodes 6 and 7 in a new second QCM sensor 11 b, thesecond room 36 is covered with the shield portion 28 b of the shutter28.

FIG. 14B illustrates a state where the time t is between the first timet_(s) and a second time t_(c).

Since this time is within the first period T₁ described in the firstembodiment, correction is performed using both of the first and secondQCM sensors 11 a and 11 b. Thus, at this time, the first and second QCMsensors 11 a and 11 b are both exposed to the atmosphere containing thecorrosive gas by communicating the window 28 a with each of the firstand second rooms 35 and 36.

FIG. 14C illustrates a state where the time t is after the second timet_(c). At this time, as described in the first embodiment, the amount ofcorrosion caused by the corrosive gas is measured by using the newsecond QCM sensor 11 b.

Therefore, in this case, the second QCM sensor 11 b is exposed to theatmosphere containing the corrosive gas by communicating the window 28 awith the second room 36. Note that, since the measurement using thefirst QCM sensor 11 a is finished, the first room 35 housing the firstQCM sensor 11 a is covered with the shield portion 28 b.

According to this embodiment described above, as illustrated in FIGS.14A to 14C, the control unit 15 automatically selects one of the firstand second QCM sensors 11 a and 11 b that is to be exposed to theatmosphere, in accordance with the time t. Thus, burden of a user can belessened

Furthermore, the new second QCM sensor 11 b is housed in the sensor unit25 in advance, thereby reducing the labor for attaching the second QCMsensor 11 b to the drive unit 13.

Moreover, the second QCM sensor 11 b is housed in the second room 36 andnot exposed to the corrosive gas outside until the life of the first QCMsensor 11 a comes closer to the end. Thus, corrosion of the electrodes 6and 7 in the new second QCM sensor 11 b can also be prevented.

Note that, since the measurement using the first QCM sensor 11 a isfinished in the state of FIG. 14C, there is no influence on themeasurement even when the state is changed to the state of FIG. 14Binstead of the state of FIG. 14C. However, in terms of suppressingcontamination of the connectors 19 and the inside of the first room 35housing the first QCM sensor 11 a, it is preferable that the first QCMsensor 11 a is shielded with the shield portion 28 b as illustrated inFIG. 14C.

Third Embodiment

In the second embodiment, the long shutter 28 is used as illustrated inFIG. 11. Meanwhile, in this embodiment, a circular shutter is used asdescribed below.

FIG. 15 is a plan view of a sensor unit used in this embodiment.

The sensor unit 42 includes a housing 43 having a cylindrical shape in aplanar view, a circular shutter 59, and a cap 60 placed on the shutter59.

The shutter 59 is formed by overlaying two rotating plates capable ofrotating independently of each other as described later, and edge of theshutter 59 overlaps with the housing 43.

The housing 43 is formed by shaping resin or metal, and includes firstto fourth rooms 44 to 47 therein. In the first to fourth rooms 44 to 47,first to fourth QCM sensors 11 a to 11 d are housed, respectively. Notethat the QCM sensors 11 a to 11 d have the same structure as thatillustrated in FIG. 1, and thus description thereof is omitted.

Also, the cap 60 has a cross-shaped bar provided in a circular ring.

FIG. 16A is a plan view of a first rotating plate 51 used as the shutter59. FIG. 16B is a plan view of a second rotating plate 52 used togetherwith the first rotating plate 51.

As illustrated in FIG. 16A, the first rotating plate 51 has a circularshape in a planar view. Also, the first rotating plate 51 can rotateabout a first shaft 51 a, and includes a first opening 53 and a secondopening 54. The shape of the openings is not particularly limited. Inthis embodiment, the first and second openings 53 and 54 are formed tohave a fan shape extending from the first shaft 51 a toward the rim ofthe first rotating plate 51.

As illustrated in FIG. 16B, the second rotating plate 52 also has thesame circular shape as that of the first rotating plate 51.

The second rotating plate 52 can rotate about a second rotating shaft 52a and includes third and fourth openings 55 and 56 having the same shapeas that of the first and second openings 53 and 54 described above.

Note that both of the first and second rotating plates 51 and 52 aremetal plates or resin plates.

FIG. 17A is a cross-sectional view taken along the line II-II in FIG.15.

As illustrated in FIG. 17A, the first and second rotating plates 51 and52 are sequentially overlaid on an opening edge 43 a of the housing 43.

The cap 60 has an inner side surface fixed to an outer peripheral sidesurface of the housing 43. The cap 60 also slides on an upper surface ofthe second rotating plate 52, thereby suppressing rattling of the firstand second rotating plates 51 and 52.

Moreover, a desiccant 66 such as silica gel is provided in each of therooms 44 to 47. The electrodes 6 and 7 in the first to fourth QCMsensors 11 a to 11 d are corroded by a corrosive gas. The larger theamount of moisture in the atmosphere is, the faster the corrosion rateis. Therefore, by using the desiccant 66 to maintain the rooms 44 to 47in a low-relative humidity state, the life of the first to fourth QCMsensors 11 a to 11 d can be prevented from being shortened by theprogress of corrosion of the electrodes 6 and 7 in the sensors beforemonitoring the corrosive gas.

Furthermore, the desiccant 66 has the property to adsorb not onlymoisture but also the corrosive gas and the like. Thus, such an effectcan also be expected that the desiccant 66 cleans the atmosphere in eachof the rooms 44 to 47 storing the first to fourth QCM sensors 11 a to 11d.

The position to house the desiccant 66 is not limited to the above. FIG.17B is an enlarged cross-sectional view when the desiccant 66 is housedin the second rotating plate 52.

Note that, in FIG. 17B, the same components as those described withreference to FIG. 17A are denoted by the same reference numerals asthose in FIG. 17A, and description thereof is omitted below.

In the example of FIG. 17B, a recess 52 y is provided in a lower surface52 x of the second rotating plate 52, and the desiccant 66 is housed inthe recess 52 y. Note that a perforated mesh lid 58 is provided at anopening edge of the recess 52 y. The lid 58 prevents the desiccant 66from falling by gravity.

According to this, when the rooms 44 to 47 are covered with the secondrotating plate 52, the desiccant 66 can reduce the relative humidity inthese rooms.

Moreover, when the rooms 44 to 47 are released to the atmosphere throughthe third opening 55 and the fourth opening 56 by rotating the secondrotating plate 52, the desiccant 66 is trapped between the first andsecond rotating plates 51 and 52. Thus, when measurement using the QCMsensors 11 a to 11 d housed in the rooms 44 to 47 is started whileexposing the QCM sensors to the atmosphere, a relative humidity aroundthe QCM sensors 11 a to 11 d can be prevented from being lowered due tothe desiccant 66.

Meanwhile, the first and second rotating shafts 51 a and 52 a arecoaxial. The first rotating shaft 51 a is mechanically connected to afirst motor 61, and the second rotating shaft 52 a is mechanicallyconnected to a second motor 62.

FIG. 18 is an enlarged cross-sectional view of the opening edge 43 a ofthe housing 43.

As illustrated in FIG. 18, first to third smoothing members 65 to 67 areprovided at the edge of the cap 60 to increase airtightness in the firstto fourth rooms 44 to 47.

Among them, the first smoothing member 65 has an elastic body 65 a fixedto the opening edge 43 a of the housing 43 and a seal material 65 bfixed on the elastic body 65 a. The elastic body 65 a is sponge orrubber, for example, and elastically deforms itself to increase stickingforce between the first smoothing member 65 and the first rotating plate51.

Note that the elastic body 65 a may be impregnated with a desiccant suchas silica gel. Thus, the elastic body 65 a has the same function as thatof the desiccant 66 (see FIGS. 17A and 17B). Accordingly, the rooms 44to 47 can be maintained at low relative humidity to prevent unnecessarycorrosion of the electrodes 6 and 7 in the first to fourth QCM sensors11 a to 11 d.

Moreover, the seal 65 b contacts with the first rotating plate 51 toincrease the airtightness in the first to fourth rooms 44 to 47. Also,the seal 65 b reduces frictional force between the first smoothingmember 65 and the first rotating plate 51 to smoothen the rotationalmovement of the first rotating plate 51.

The material of the seal 65 b is not particularly limited. In thisembodiment, silicon resin, fluorine resin or the like with goodsmoothness is used as the material of the seal 65 b.

Meanwhile, the second smoothing member 66 is fixed to an upper surfaceof the first rotating plate 51 and is in contact with a rim of thesecond rotating plate 52 to reduce frictional force between the firstand second rotating plates 51 and 52. Likewise, the third smoothingmember 67 is fixed to the upper surface of the second rotating plate 52to reduce frictional force between the second rotating plate 52 and thecap 60.

As the material of the second and third smoothing members 66 and 67,silicon resin, fluorine resin or the like can be used, for example.

FIG. 19 is a configuration diagram of an environmental measurementapparatus 70 including the sensor unit 42. Note that, in FIG. 19, thesame components as those described with reference to FIG. 13 in thesecond embodiment are denoted by the same reference numerals as those inFIG. 13, and description thereof is omitted below.

As illustrated in FIG. 19, a drive unit 13 includes first to fourthoscillation circuits 16 a to 16 d and first to fourth frequency counters18 a to 18 d corresponding to the first to fourth QCM sensors 11 a to 11d, respectively.

Among them, the third and fourth oscillation circuits 16 c and 16 d arecircuits to resonate the third and fourth QCM sensors 11 c and 11 d in afundamental wave mode, and have the same circuit configuration as thatillustrated in FIG. 4.

The third frequency counter 18 c is connected to the third oscillationcircuit 16 c, and measures a third oscillation frequency f_(3m) of thethird QCM sensor 11 c. Likewise, the fourth frequency counter 18 d isconnected to the fourth oscillation circuit 16 d, and measures a fourthoscillation frequency f_(4m) of the fourth QCM sensor 11 d.

Furthermore, a control unit 15 to control rotation amounts of the firstand second motors 61 and 62 (see FIG. 17A) is provided at the laterstage of the operation unit 14.

Next, operations of the sensor unit 42 are described.

FIGS. 20A to 20C, 21A to 21C, and 22A to 22C are plan views forexplaining the operations of the sensor unit 42.

Among them, FIGS. 20A to 20C illustrate a state where a time t is beforea first time t_(s). FIG. 20A is a plan view of the sensor unit 42, FIG.20B is a plan view of the first rotating plate 51, and FIG. 20C is aplan view of the second rotating plate 52.

At this time, as described in the first embodiment, the first QCM sensor11 a is not close to the end of its life yet, and the amount ofcorrosion caused by the corrosive gas is measured by using only thefirst QCM sensor 11 a.

Thus, at this time, by adjusting the rotation amounts of the first andsecond rotating plates 51 and 52, the first opening 53 and the fourthopening 56 are overlaid over the first room 44 to form a window W bythese openings, and the first QCM sensor 11 a is exposed from the windowW.

Also, in order to prevent corrosion of the electrodes 6 and 7 of newsecond to fourth QCM sensors 11 b to 11 d, the second to fourth rooms 45to 47 are covered with at least one of the first and second rotatingplates 51 and 52.

FIGS. 21A to 21C illustrate a state where the time t is between thefirst time t_(s) and a second time t_(c). FIG. 21A is a plan view of thesensor unit 42, FIG. 21B is a plan view of the first rotating plate 51,and FIG. 21C is a plan view of the second rotating plate 52.

Since this time is within a first period T₁ described in the firstembodiment, correction is performed using both of the first and secondQCM sensors 11 a and 11 b.

Thus, at this time, the first opening 53 and the third opening 55 areoverlaid over the first room 44, and the second opening 54 and thefourth opening 56 are overlaid over the second room 45. Accordingly,windows W are formed by the first to fourth openings 53 to 56, and thefirst and second QCM sensors 11 a and 11 b are exposed from the windowsW.

Note that the third and fourth rooms 46 and 47 are covered with thefirst and second rotating plates 51 and 52, in order to preventcorrosion of the electrodes 6 and 7 of the third and fourth QCM sensors11 c and 11 d housed therein.

FIGS. 22A to 22C illustrate a state where the time t is after the secondtime t_(c). FIG. 22A is a plan view of the sensor unit 42, FIG. 22B is aplan view of the first rotating plate 51, and FIG. 22C is a plan view ofthe second rotating plate 52.

At this time, as described in the first embodiment, the amount ofcorrosion is measured by using the new second QCM sensor 11 b.

Thus, in this case, a window W is formed by overlaying the first opening53 and the fourth opening 56 over the second room 45, and the second QCMsensor 11 b is exposed from the window W.

Also, in order to prevent corrosion of the electrodes 6 and 7 of the newthird and fourth QCM sensors 11 c and 11 d, the third and fourth rooms46 and 47 are covered with at least one of the first and second rotatingplates 51 and 52.

Furthermore, since there is no need to expose the first QCM sensor 11 athat has come to the end of its life to the atmosphere, the first room44 is covered with at least one of the first and second rotating plates51 and 52.

Thereafter, when the life of the second QCM sensor 11 b comes close tothe end, the third QCM sensor 11 c takes over the measurement.Furthermore, when the life of the third QCM sensor 11 c comes close tothe end, the fourth QCM sensor 11 d takes over the measurement. Acorrection method during the taking over is the same as that in thefirst embodiment, and the movement of the rotating plates 51 and 52 isthe same as those illustrated in FIGS. 20A to 20C, 21A to 21C, and 22Ato 22C. Thus, description thereof is omitted.

According to this embodiment described above, as in the case of thesecond embodiment, it is automatically selected which one of the firstto fourth QCM sensors 11 a to 11 d is to be exposed to the atmosphere.Thus, the burden of a user can be lessened.

Furthermore, the number of the QCM sensors that can be housed in onesensor unit 42 is four, which is larger than in the second embodiment.Thus, the corrosive gas in the atmosphere can be monitored over a longertime period by sequentially using the first to fourth QCM sensors 11 ato 11 d.

Fourth Embodiment

In the first embodiment, the first specified value F_(sm) is used as acriterion for determining whether or not the life of the first QCMsensor 11 a is close to the end in Step S2 as illustrated in FIG. 7.

The first specified value F_(sm) is a specified value predetermined forthe first change Δf_(1m) in the first oscillation frequency f_(1m) ofthe first QCM sensor 11 a. Alternatively, the life of the first QCMsensor 11 a may be determined as follows.

FIG. 23 is a plan view of a first QCM sensor 11 a according to thisembodiment. Note that, in FIG. 23, the same components as thosedescribed in the first embodiment are denoted by the same referencenumerals as those in the first embodiment, and description thereof isomitted below.

As illustrated in FIG. 23, in this embodiment, a wire 9 independent of afirst electrode 6 is provided on a main surface of a crystal oscillator5, and an operation unit 14 (see FIG. 3) measures a resistance value Rof a wire 9. Note that the wire 9 may be provided on another mainsurface of the crystal oscillator 5, which is opposite to the firstelectrode 6.

When the first QCM sensor 11 a is placed in a corrosive gas atmosphere,not only the first electrode 6 but also the wire 9 is corroded,resulting in an increase in the resistance value R of the wire 9.Therefore, by monitoring the resistance value R of the wire 9, one canestimate how much of the first electrode 6 is corroded. Thus, it can bepredicted whether the life of the first QCM sensor 11 a is close to theend or not.

The material of the wire 9 is not particularly limited. However, it ispreferable that the wire 9 is formed of the same material as that thecorrosion is wished to be measured, such as silver or copper used as thematerial of the first electrode 6. By using the same material as that ofthe first electrode 6, the wire 9 and the first electrode 6 have thesame corrosion rate. Thus, the life of the first QCM sensor 11 a can beaccurately predicted based on the resistance value R of the wire 9.

A processing method in Step S2 (see FIG. 7) in this embodiment is alsonot particularly limited. For example, a threshold value R₁ may be setfor the resistance value R of the wire 9, and the operation unit 14 maydetermine in Step S2 whether or not the resistance value R is equal toor more than the threshold value R₁.

Here, when it is determined that the resistance value R is equal to ormore than the threshold value R₁ (YES), the life of the first QCM sensor11 a is close to the end, and thus the processing goes to Step S3according to the first embodiment. On the other hand, when it isdetermined that the resistance value R is not equal to or more than thethreshold value R₁ (NO), the life of the first QCM sensor 11 a is notclose to the end yet, and thus the processing return to Step S1 as inthe case of the first embodiment.

According to this embodiment described above, the life of the first QCMsensor 11 a can be easily predicted by measuring the resistance value Rof the wire 9 formed in the first QCM sensor 11 a.

Fifth Embodiment

In this embodiment, QCM sensors are corrected by using a dedicated QCMsensor for correction as described below.

FIG. 24 is a configuration diagram of an environmental measurementapparatus according to this embodiment. Note that, in FIG. 24, the samecomponents as those described with reference to FIG. 3 are denoted bythe same reference numerals as those in FIG. 3, and description thereofis omitted below.

As illustrated in FIG. 24, in the environmental measurement apparatus70, a first QCM sensor 11 a and a second QCM sensor 11 b are attached toa drive unit 13 as in the case of the first embodiment.

The first QCM sensor 11 a is the dedicated sensor for correction, and ishoused in a sensor unit 71. The sensor unit 71 exposes the first QCMsensor 11 a to the atmosphere only when performing correction asdescribed later, and separates the first QCM sensor 11 a from theatmosphere when performing no correction.

Meanwhile, the second QCM sensor 11 b is used to monitor the amount ofcorrosion caused by a corrosive gas in the atmosphere, and is replacedwith a new QCM sensor when the life thereof approaches the end.

FIG. 25 is a perspective view of the sensor unit 71. Note that, in FIG.25, the same components as those described with reference to FIGS. 10 to12 are denoted by the same reference numerals as those in FIGS. 10 to12, and description thereof is omitted below.

In the sensor unit 71, a shutter 28 is moved in a longitudinal directionthereof by rotation of a motor 27. By controlling the amount of movementof the shutter 28, the first QCM sensor 11 a can be exposed from awindow 28 a of the shutter 28, and an opening 26 a in a housing 26 canbe covered with a shield portion 28 b of the shutter 28.

FIG. 26 is a cross-sectional view taken along the line III-III in FIG.25.

In this embodiment, only one first QCM sensor 11 a is housed in thesensor unit 71. Therefore, the partition plate 32 as illustrated in FIG.12 is not required, and only one room is defined in the housing 26.

FIG. 27 is an enlarged view of the second QCM sensor 11 b and the driveunit 13.

As illustrated in FIG. 27, the drive unit 13 is provided with twoconnectors 19, to and from which two conductive wires 8 in the secondQCM sensor 11 b can be attached and detached.

In this embodiment, when the second QCM sensor 11 b comes to the end ofits life, a user detaches the second QCM sensor 11 b from the connectors19 and attaches a new third QCM sensor 11 c to the connectors 19.

The specifications of the first to third QCM sensors 11 a to 11 c arenot particularly limited. However, in this embodiment, the first tothird QCM sensors 11 a to 11 c have the same specifications, in order toaccurately grasp variations in the amount of corrosion caused by thecorrosive gas before and after the replacement of the old and new QCMsensors. Note that, as already mentioned, the specifications of the QCMsensors include the size and pane of the crystal oscillator 5, the sizeand material of each of the first and second electrodes 6 and 7, and thelike, for example.

Next, an environmental measurement method according to this embodimentis described.

FIG. 28 is a diagram illustrating an example of measurement results ofthe first to third QCM sensors 11 a to 11 c. In FIG. 28, first to thirdgraphs A₁ to A₃ correspond to the measurement results of the first tothird QCM sensors 11 a to 11 c, respectively.

The horizontal axis of each of the graphs represents time that haselapsed since the start of measurement with the second QCM sensor 11 b.Also, the vertical axis of each graph represents first to third changesΔf_(1m) to Δf_(3m), which are changes in an oscillation frequency ofeach of the first to third QCM sensors 11 a to 11 c respectively.

Note that the third change Δf_(3m) is defined by Δf_(3m)=F₃−f_(3m) usinga third oscillation frequency f_(3m) of the third QCM sensor 11 c. Here,F₃ is a fundamental frequency of the third QCM sensor 11 c.

As illustrated in FIG. 28, in this embodiment, a second period T₂ isprovided, during which the measurement is conducted with both of thefirst and third QCM sensors 11 a and 11 c, besides a first period T₁during which the measurement is conducted with both of the first andsecond QCM sensors 11 a and 11 b.

A first time t_(s), which is the beginning of the first period T₁, isthe time when the second change Δf_(2m) in the oscillation frequency ofthe second QCM sensor 11 b reaches a predetermined first specified valueF_(sm). A second time t_(c), which is the end of the first period T₁, isthe time when the second change Δf_(2m) reaches a predetermined secondspecified value F_(cm).

A third time t_(d), which is the beginning of the second period T₂, isthe time to start acquiring the third oscillation frequency f_(3m) ofthe third QCM sensor 11 c. A fourth time t_(e), which is the end of thesecond period T₂, is the time to end the acquisition of the firstoscillation frequency f_(1m) of the first QCM sensor 11 a.

Here, since the first and second QCM sensors 11 a and 11 b have the samespecifications as described above, the first and second graphs A₁ and A₂are expected to have the same slope during the first period T₁. However,the individual difference of the first and second QCM sensors 11 a and11 b actually cause a difference in slope between the graphs A₁ and A₂during the first period T₁ as illustrated in FIG. 28.

For the same reason, the first and third graphs A₁ and A₃ have differentslopes during the second period T₂.

In order to prevent inaccurate results of measurement of the amount ofcorrosion caused by the corrosive gas in the atmosphere due to suchindividual difference, the measurement values of the second and thirdQCM sensors 11 b and 11 c are corrected as follows in this embodiment.

FIG. 29 is a flowchart for explaining an environmental measurementmethod according to this embodiment.

In the first Step S20, an operation unit 14 acquires the secondoscillation frequency f_(2m) of the second QCM sensor 11 b at a time t,and calculates the second change Δf_(2m) in the oscillation frequencyf_(2m) at the time t. The second change Δf_(2m) is a difference(F₂−f_(2m)) between the fundamental frequency F₂ which is theoscillation frequency of the second QCM sensor 11 b at a time 0 and thesecond oscillation frequency f_(2m) at the time t.

Next, in Step S21, the operation unit 14 determines whether or not thesecond change Δf_(2m) is equal to or more than the first specified valueF_(sm).

Here, when it is determined that the second change Δf_(2m) is not equalto or more than the first specified value F_(sm) (NO), the second QCMsensor 11 b is considered to be not close to the end of its life yet.Thus, the processing returns to Step S20 to continue the measurementusing the second QCM sensor 11 b.

On the other hand, when it is determined in Step S21 that the secondchange Δf_(2m) is equal to or more than the first specified value F_(sm)(YES), it is considered that the time t is within the first period T₁described above and the life of the second QCM sensor 11 b is comingclose to the end.

Therefore, in this case, the processing goes to Step S22 to prepare forcorrection using the first QCM sensor 11 a by driving the motor 27 (seeFIG. 25) under the control of a control unit 15 to move the shutter 28and exposing the first QCM sensor 11 a from the window 28 a.

Next, in Step S23, the operation unit 14 starts acquiring the firstoscillation frequency f_(1m) of the first QCM sensor 11 a. Consideringthe time needed for moving the shutter 28 (see FIG. 25), the start timeis slightly behind the first time t_(s). However, the acquisition of thefirst oscillation frequency f_(1m) is substantially started from thefirst time t_(s).

Then, the operation unit 14 starts calculating the first change Δf_(1m)in the first oscillation frequency f_(1m) at the time t. The firstchange Δf_(1m) is a difference (F₁-f_(1m)) between the fundamentalfrequency F₁ which is the oscillation frequency of the first QCM sensor11 a at the first time t_(s) and the first oscillation frequency f_(1m)at the time t.

Next, in Step S24, the operation unit 14 determines whether or not thefirst change Δf_(1m) is equal to or more than the second specified valueF_(cm) described above.

Here, when it is determined that the first change Δf_(1m) is not equalto or more than the second specified value F_(cm) (NO), it is consideredthat the life of the second QCM sensor 11 b is approaching the end butdoes not yet reach the end. Thus, the processing returns to Step S23.

On the other hand, when it is determined in Step S24 that the firstchange Δf_(1m) is equal to or more than the second specified valueF_(cm) (YES), it is considered that the second QCM sensor 11 b come tothe end of its life.

Thus, in this case, the processing goes to Step S25 to end themeasurement carried out by the second QCM sensor 11 b at the second timet_(c), at which the second change Δf_(2m) becomes equal to the secondspecified value F_(cm).

Thereafter, in Step S26, the operation unit 14 calculates a firstcorrection coefficient C₁ to retrospectively correct the second changeΔf_(2m) at or before the second time t_(c).

FIG. 30 is a diagram for explaining a method for calculating the firstcorrection coefficient C₁. In FIG. 30, the first graph A₁ illustrated inFIG. 28 is subjected to an upward parallel translation, thereby matchingthe starting point of the first graph A₁ with the second graph A₂ at thefirst time t_(s).

Moreover, the third graph A₃ is also subjected to an upward paralleltranslation to match the starting point thereof with the first graph A₁at the third time t_(d).

Due to differences in slope among the first to third graphs A₁ to A₃,mere parallel translation like this cannot connect each graphs.

In this step, in order to resolve such a difference in slope between thefirst and second graphs A₁ and A₂ among the graphs, the operation unit14 calculates the first correction coefficient C₁ by which the secondchange Δf_(2m) is to be multiplied as follows.

First, a first increment F_(c)−F_(s) of the first change Δf_(1m) withinthe first period T₁ and a second increment F_(cm)−F_(sm) of the secondchange Δf_(2m) within the first period T₁ are calculated. Note thatF_(s) is the value of the first change Δf_(1m) at the first time t_(s),and F_(c) is the value of the first change Δf_(1m) at the second timet_(c).

Then, the operation unit 14 calculates a first ratio(F_(c)−F_(s))/(F_(cm)−F_(sm)) of the first increment F_(c)−F_(s) to thesecond increment F_(cm)−F_(sm), and sets the first ratio as the firstcorrection coefficient C₁. The first correction coefficient C₁ thuscalculated is equal to a ratio between the slopes of the second andfirst graphs A₂ and A₁ in FIG. 28 during the first period T₁.

Then, in Step S27, the operation unit 14 retrospectively corrects thealready calculated second change Δf_(2m) by multiplying the secondchange Δf_(2m) at or before the first time t_(s) by the first correctioncoefficient C₁.

As described above, the first correction coefficient C₁ is equal to theratio between the slopes of the graphs A₁ and A₂. Therefore, bymultiplying the second change Δf_(2m) by the first correctioncoefficient C₁ in this step, the graph A₂ can be corrected to match theslope thereof with the slope of the graph A₁.

Moreover, during the first period T₁, the corrosion of the second QCMsensor 11 b progresses considerably and thus the slope of the secondgraph A₂ is stabilized. As a result, errors are less likely to occur inthe second increment F_(cm)−F_(sm), and the second change Δf_(2m) can beaccurately corrected in this step.

Next, in Step S28, the user detaches the second QCM sensor 11 b from theconnectors 19 (see FIG. 27), and attaches a new third QCM sensor 11 c tothe connectors 19.

Then, in Step S29, the operation unit 14 starts acquiring the thirdoscillation frequency f_(3m) of the third QCM sensor 11 c at the thirdtime t_(d), and calculates the third change Δf_(3m) in the thirdoscillation frequency f_(3m) at the time t.

As already mentioned, the third change Δf_(3m) at the time t is definedby Δf_(3m)=F₃−f_(3m) using the fundamental frequency F₃ of the third QCMsensor 11 c and the third oscillation frequency f_(3m) at the time t.

Thereafter, in Step S30, the operation unit 14 determines whether or notthe third change Δf_(3m) is equal to or more than the predeterminedthird specified value F_(em).

The third specified value F_(em) is served as the clue to determinewhether one can obtain the third change Δf_(3m) which is large enough tocorrect the third QCM sensor 11 c, and is preset by the user. Moreover,as presented in FIG. 30, the third specified value F_(em) also has ameaning of an increment of the third graph A₃ during the second periodT₂, i.e., a third increment of the third change Δf_(3m).

Here, when it is determined that the third change Δf_(3m) is not equalto or more than the third specified value F_(em) (NO), since themagnitude of the third change Δf_(3m) is not sufficient yet, theprocessing returns to Step S29 again.

On the other hand, when it is determined in Step S30 that the thirdchange Δf_(3m) is equal to or more than the third specified value F_(em)(YES), the processing goes to Step S31. In Step S31, the motor 27 (seeFIG. 25) is driven under the control of the control unit 15 to move theshutter 28, and the first QCM sensor 11 a is shielded with the shieldportion 28 b of the shutter 28.

Accordingly, the acquisition of the first oscillation frequency f_(1m)of the first QCM sensor 11 a, which has started in Step S23, iscompleted.

Moreover, by covering the opening 26 a with the shutter 28 in thismanner, the electrodes 6 and 7 in the first QCM sensor 11 a can beseparated from the outside air. As a result, the progress of thecorrosion of the electrodes 6 and 7 due to the corrosive gas containedin the outside air is stopped. Thus, the life of the first QCM sensor 11a can be extended.

Next, the processing goes to Step S32. In Step S32, as illustrated inFIG. 30, the operation unit 14 calculates a first increment F_(e)−F_(d)of the first change Δf_(1m) within the second period T₂ and a thirdincrement F_(em) of the third change Δf_(3m) within the second periodT₂.

Furthermore, the operation unit 14 calculates a second ratio(F_(e)−F_(d))/F_(em) of the first increment F_(e)−F_(d) to the thirdincrement F_(em), and sets the second ratio as a second correctioncoefficient C₂. The second correction coefficient C₂ thus calculated isequal to a ratio between the slopes of the first and third graphs A₁ andA₃ in FIG. 28 during the second period T₂.

Then, in Step S33, the operation unit 14 corrects the third changeΔf_(3m) by multiplying the third change Δf_(3m) at and after the thirdtime t_(d) by the second correction coefficient C₂.

As described above, the second correction coefficient C₂ is equal to theratio between the slopes of the graphs A₁ and A₃. Therefore, bymultiplying the third change Δf_(3m) by the second correctioncoefficient C₂ in this step, the graph A₃ can be corrected to match theslope thereof with the slope of the graph A₁.

Furthermore, in order to match the height of the third graph A₃ withthat of the corrected first graph A₁, the operation unit 14 furthercorrects the third change Δf_(3m) as indicated by the following equation(2).Δf _(3m) ←C ₂ ×Δf _(3m) +C ₁ ×F _(cm)+(F _(d) −F _(c))  (2)

The second term in the right-hand side of the equation (2) is the valueof the second graph A₂ at the second time t_(c), which is corrected inStep S27. The third term in the right-hand side is an increment of thefirst graph A₁ between the second time t_(c) and the third time t_(d).By adding these two terms to the corrected value (C₂×Δf_(3m)) describedabove, the height of the third graph A₃ can be matched with that of thecorrected first graph A₁ while taking into consideration the incrementof the first graph A₁.

Next, in Step S34, the operation unit 14 uses the correction valuescalculated in Steps S27 and S33 described above to generate measurementvalues at all the times t as follows.

First, when the time t is before the second time t_(c), the value(C₁×Δf_(2m)) calculated in Step S27 is used as the measurement value atthe time t.

When the time t is between the second time t_(c) and the third timet_(d), Δf_(1m)+C₁×F_(cm) is used as the measurement value.

When the time t is after the third time t_(d), the corrected value(C₂×Δf_(3m)+C₁×F_(cm)+(F_(d)−F_(c))) of equation (2) is used as themeasurement value.

FIG. 31 is a graph obtained by the measurement values generated in thisstep. Note that the horizontal axis and vertical axis of this graph meanthe same as those described with reference to FIG. 28, and thusdescription thereof is omitted here.

In FIG. 31, portions corresponding to the first to third graphs A₁ to A₃before the correction are denoted by reference numerals A₁ to A₃. Also,F₀₁ to F₀₄ represent values of the graphs corresponding to the first tofourth times t_(s) to t_(e).

As illustrated in FIG. 31, the measurement values can be continuouslyacquired throughout the all times t by performing the correction asdescribed above.

FIG. 32 is an enlarged view of the graph illustrated in FIG. 31 at thefirst to fourth times t_(s) to t_(e).

As illustrated in FIG. 32, the graphs at the first to fourth times t_(s)to t_(e) are smoothly connected by the above correction.

Thus, the basic steps of the environmental measurement method accordingto this embodiment are completed.

According to this embodiment described above, the first QCM sensor 11 ais used as the dedicated sensor for correction. Thus, the measurementvalues can be continuously acquired throughout the all times t asillustrated in FIG. 31 by correcting the second change Δf_(2m) of thesecond QCM sensor 11 b and the third change Δf_(3m) of the third QCMsensor 11 c.

Moreover, the life of the first QCM sensor 11 b can also be extended byusing the first QCM sensor 11 b only for the purpose of correction andseparating the first QCM sensor 11 b from the atmosphere when performingno correction.

Furthermore, the first QCM sensor 11 b used only for correction isexposed to the atmosphere every time the correction is performed, andhence the corrosion of the electrodes 6 and 7 progresses to some extent.Therefore, the characteristics of the first QCM sensor 11 b arestabilized as in the case of performing the aging treatment.Accordingly, the correction accuracy is improved by correcting thesecond change Δf_(2m) and the third change Δf_(3m) based on the firstQCM sensor 11 b as in this embodiment.

Sixth Embodiment

In the fifth embodiment, the user replaces the second QCM sensor 11 b,whose life has come to the end, with the new third QCM sensor 11 c byuser's own hand in Step S28 of FIG. 29. In this embodiment, thereplacement is automatically performed as follows.

FIG. 33 is a plan view of a sensor unit 80 used in this embodiment. Notethat, in FIG. 33, the same components as those described with referenceto FIG. 15 are denoted by the same reference numerals as those in FIG.15, and description thereof is omitted below.

The sensor unit 80 includes a housing 43 having a cylindrical shape in aplanar view, a circular shutter 59 made of resin or metal, and a cap 60covering the shutter 59.

In the housing 43, first to fourth rooms 44 to 47 are provided.

The positions of the rooms are not particularly limited. In thisembodiment, the second room 45 is provided on one of the sides of thefirst room 44, and the third room 46 is provided on the other sidethereof. Also, the fourth room 47 is provided adjacent to both of thesecond room 45 and the third room 46.

The first to third QCM sensors 11 a to 11 c are housed in the first tothird rooms 44 to 46, respectively. Note that no QCM sensor is housed inthe fourth room 47 in this embodiment.

Although the shutter 59 includes the two rotating plates 51 and 52 asillustrated in FIG. 15 in the third embodiment, the shutter 59 of thisembodiment includes only one rotating plate.

FIG. 34 is a plan view of the shutter 59.

As illustrated in FIG. 34, the shutter 59 has a circular shape in theplanar view, and can rotate about a shaft 59 a. Moreover, a first window81 and a second window 82 are formed in the shutter 59. A portion of theshutter 59, in which the windows are not formed, is served as a shieldportion 59 b to cover the first to fourth rooms 44 to 47.

The first and second windows 81 and 82 are formed so as to correspond totwo adjacent rooms of the first to fourth rooms 44 to 47. Thus, twoadjacent rooms selected from the first to fourth rooms 44 to 47communicate with the first and second windows 81 and 82, and theremaining non-selected rooms are covered with the shield portion 59 b.

FIG. 35 is a cross-sectional view taken along the line IV-IV in FIG. 33.

The cap 60 has an inner side surface mechanically fixed to an outerperipheral side surface of the housing 43. The cap 60 slides on an uppersurface of the shutter 59, thereby suppressing rattling of the shutter59.

Meanwhile, the shaft 59 a is mechanically connected to a motor 86, andcan rotate the shutter 59 by rotation of the motor 86.

Note that a desiccant 66 (see FIGS. 17A and 17B) described in the thirdembodiment may be placed in each of the rooms 44 to 46 to preventcorrosion of electrodes 6 and 7 in the first to third QCM sensors 11 ato 11 c from being promoted by moisture.

FIG. 36 is a configuration diagram of an environmental measurementapparatus including the sensor unit 80. Note that, in FIG. 36, the samecomponents as those described with reference to FIGS. 19, 20A to 20C,21A to 21C, 22A to 22C, 23 and 24 are denoted by the same referencenumerals as those in these figures, and description thereof is omittedbelow.

As illustrated in FIG. 36, the first to third QCM sensors 11 a to 11 cin the sensor unit 80 are connected to a control unit 15 through a driveunit 13 and an operation unit 14. In this embodiment, the control unit15 adjusts a rotation amount of the shutter 59 by controlling a rotationamount of the motor 86.

Next, operations of the sensor unit 80 are described.

FIGS. 37A to 37D are plan views for explaining the operations of thesensor unit 80.

FIG. 37A illustrates a state where the time t is before the first timet_(s). At this time, as described in the fifth embodiment, the secondQCM sensor 11 b is not close to the end of its life yet, and the amountof corrosion caused by a corrosive gas is measured by using only thesecond QCM sensor 11 b.

Thus, at this time, the second window 82 communicates with the secondroom 45 by adjusting the rotation amount of the shutter 59, and thesecond QCM sensor 11 b is exposed from the second window 82.

Moreover, in order to prevent the corrosion of the electrodes 6 and 7 inthe first QCM sensor 11 a for correction and the new third QCM sensor 11c, the first and third rooms 44 and 46 are covered with the shieldportion 59 b.

FIG. 37B illustrates a state where the time t is between the first timet_(s) and the second time t_(e).

Since this time is within the first period T₁ described in the fifthembodiment, correction is performed using both of the first and secondQCM sensors 11 a and 11 b.

Therefore, at this time, the first and second QCM sensors 11 a and 11 bare exposed from the windows 81 and 82 by communicating the secondopening 82 with the first room 44 and communicating the first opening 81with the second room 45.

Note that the third room 46 is covered with the shield portion 59 b toprevent the corrosion of the electrodes 6 and 7 in the third QCM sensor11 c housed therein.

FIG. 37C illustrates a state where the time t is between the third timet_(d) and the fourth time t_(e).

Since this time is within the second period T₂ described in the fifthembodiment, correction is performed using both of the first and thirdQCM sensors 11 a and 11 c.

Therefore, at this time, the first and third QCM sensors 11 a and 11 care exposed from the windows 81 and 82 by communicating the firstopening 81 with the first room 44 and communicating the second opening82 with the third room 46.

Furthermore, since there is no need to expose the second QCM sensor 11 bthat has come to the end of its life to the atmosphere, the second room45 is covered with the shield portion 59 b.

FIG. 37D illustrates a state where the time t is after the fourth timet_(e).

At this time, as described in the fifth embodiment, the amount ofcorrosion caused by the corrosive gas is measured by using only thethird QCM sensor 11 c. Therefore, in this case, the third QCM sensor 11c is exposed from the first window 81 by communicating the first window81 with the third room 46.

Moreover, in order to prevent the electrodes 6 and 7 in the first QCMsensor 11 a for correction from being corroded by the corrosive gas inthe atmosphere, the first room 44 is covered with the shield portion 59b. Furthermore, since there is no need to expose the second QCM sensor11 b that has come to the end of its life to the atmosphere, the secondroom 45 is also covered with the shield portion 59 b.

According to this embodiment described above, the new third QCM sensor11 c for replacement is provided in the sensor unit 80 in advance.Therefore, when the second QCM sensor 11 b comes to the end of its life,the user does not need to attach or detach the sensors by user's ownhand. Thus, the burden on the user can be reduced.

Moreover, a mechanism to rotate the shutter 59 is very simple.Therefore, one can easily select one of the first to third QCM sensors11 a to 11 c that is to be exposed to the atmosphere.

Seventh Embodiment

Although the rotating plate is used as the shutter 59 illustrated inFIG. 33 in the sixth embodiment, a film-like shutter is used in thisembodiment.

FIG. 38A is a plan view of a sensor unit 90 used in this embodiment.FIG. 38B is a cross-sectional view taken along the line V-V in FIG. 38A.

Note that, in FIGS. 38A and 38B, the same components as those describedwith reference to FIGS. 10 to 12 are denoted by the same referencenumerals as those in FIGS. 10 to 12, and description thereof is omittedbelow.

As illustrated in FIG. 38A, in the sensor unit 90, a shutter 28 is movedin a longitudinal direction thereof by rotation of a motor 27.

A first window 28 c is provided in the shutter 28. By controlling theamount of movement of the shutter 28, the first to third QCM sensors 11a to 11 c can be exposed from the first window 28 c or an opening 26 ain a housing 26 can be covered with a shield portion 28 b of the shutter28.

Also, as illustrated in FIG. 38B, four partition plates 32 described inthe first embodiment are provided in the housing 26, and first to thirdrooms 91 to 93 are defined by the partition plates 32.

Note that, in this embodiment, ends of the partition plates 32 areconnected by a bottom plate 73, and the bottom plate 73 defines bottomsof the first to third rooms 91 to 93.

FIG. 39 is a development diagram of the shutter 28.

In the shutter 28, the first window 28 c and a second window 28 d areformed with a space therebetween. The first window 28 c is used toexpose one or two QCM sensors selected from the first to third QCMsensors 11 a to 11 c. Meanwhile, the second window 28 d is used toexpose only the first QCM sensor 11 a used for correction.

FIG. 40 is a configuration diagram of an environmental measurementapparatus 100 including the sensor unit 90. Note that, in FIG. 40, thesame components as those described with reference to FIG. 36 in thesixth embodiment are denoted by the same reference numerals as those inFIG. 36, and description thereof is omitted below.

As illustrated in FIG. 40, the first to third QCM sensors 11 a to 11 cin the sensor unit 90 are connected to a control unit 15 through a driveunit 13 and an operation unit 14. In this embodiment, the control unit15 adjusts a movement amount of the shutter 28 by controlling a rotationamount of the motor 27.

Next, operations of the sensor unit 100 are described.

FIGS. 41A to 41E are plan views for explaining the operations of thesensor unit 100.

FIG. 41A illustrates a state where the time t is before a first timet_(s). At this time, as described with reference to FIG. 28, the secondQCM sensor 11 b is not close to the end of its life yet, and the amountof corrosion caused by a corrosive gas is measured by using only thesecond QCM sensor 11 b.

Thus, at this time, the second QCM sensor 11 b is exposed to theatmosphere containing the corrosive gas by communicating the firstwindow 28 c in the shutter 28 with only the second room 92. Moreover, inorder to prevent the corrosion of electrodes 6 and 7 in the first QCMsensor 11 a for correction and a new third QCM sensor 11 c, the firstand third rooms 91 and 93 are covered with the shield portion 28 b ofthe shutter 28.

FIG. 41B illustrates a state where the time t is between the first timet_(s) and a second time t_(c).

Since this time is within a first period T₁ in FIG. 28, correction isperformed using both of the first and second QCM sensors 11 a and 11 b.

Thus, at this time, the first and second QCM sensors 11 a and 11 b areexposed from the first window 28 c by communicating the first window 28c with both of the first and second rooms 91 and 92.

Note that the third room 93 is covered with the shield portion 28 b toprevent the corrosion of the electrodes 6 and 7 in the new third QCMsensor 11 c.

FIG. 41C illustrates a state where the time t is between the second timet_(c) and a third time t_(d).

At this time, as illustrated in FIG. 28, measurement is performed usingonly the first QCM sensor 11 a for correction. Therefore, the first QCMsensor 11 a is exposed from the second window 28 d by communicating onlythe second window 28 d, which is formed to have a size to expose onlyone sensor, with the first room 91.

FIG. 41D illustrates a state where the time t is between the third timet_(d) and a fourth time t_(e).

Since this time is within a second period T₂ described with reference toFIG. 28, correction is performed using both of the first and third QCMsensors 11 a and 11 c.

Therefore, at this time, the first and third QCM sensors 11 a and 11 care exposed from the first window 28 c by communicating the first window28 c with both of the first and third rooms 91 and 93.

FIG. 41E illustrates a state where the time t is after the fourth timet_(e).

At this time, as illustrated in FIG. 28, the amount of corrosion causedby the corrosive gas is measured by using only the third QCM sensor 11c. Therefore, in this case, the third QCM sensor 11 c is exposed fromthe first window 28 c by communicating the first window 28 c with thethird room 93.

Moreover, in order to prevent the electrodes 6 and 7 in the first QCMsensor 11 a for correction from being corroded by the corrosive gas inthe atmosphere, the first room 91 is covered with the shield portion 28b. Furthermore, since there is no need to expose the second QCM sensor11 b that comes to the end of its life to the atmosphere, the secondroom 92 is also covered with the shield portion 28 b.

According to this embodiment described above, which one of the first tothird QCM sensors 11 a to 11 c is to be exposed to the atmosphere isautomatically selected according to the time t, as illustrated in FIGS.41A to 41E. Thus, the burden on the user can be reduced.

Furthermore, the first to third QCM sensors 11 a to 11 c are housed in ahousing 26 in advance. Therefore, labor for replacing the sensors can bereduced, and hence the labor on the user can be further lessened.

Eighth Embodiment

In the fifth embodiment, as illustrated in FIG. 28, the first period T₁is provided when the life of the second QCM sensor 11 b is about to end,and the second change Δf_(2m) is corrected using the first changeΔf_(1m) in the first period T₁.

Meanwhile, in this embodiment, a second change Δf_(2m) is correctedusing a first change Δf_(1m) immediately after measurement with a secondQCM sensor 11 b is started.

FIG. 42 is a diagram illustrating an example of measurement results of afirst and the second QCM sensors 11 a and 11 b (see FIG. 24). In FIG.42, first and second graphs A₁ and A₂ correspond to the measurementresults of the first and second QCM sensors 11 a and 11 b, respectively.

Note that the horizontal axis of each of the graphs represents time thathas elapsed since an arbitrary time. Also, the vertical axis of eachgraph represents first and second changes Δf_(1m) and Δf_(2m), which arechanges in an oscillation frequency of each of the first and second QCMsensors 11 a and 11 b.

As illustrated in FIG. 42, in this embodiment, a third period T₃ isprovided. The third period T₃ is provided at the early stage of themeasurement using the second QCM sensor 11 b, namely, at the beginningof a series of continuous measurements. In the third period T₃,measurement is performed using both of the second QCM sensor 11 b andthe first QCM sensor 11 a for correction.

A fifth time t_(f) which is the beginning of the third period T₃, is thetime to start acquiring the second oscillation frequency f_(2m) of thesecond QCM sensor 11 b. Also, the fifth time t_(f) is the time for theoperation unit 14 (see FIG. 24) to start calculating the second changeΔf_(2m) in the second oscillation frequency f_(2m). This time is equalto the time to start acquiring the first oscillation frequency f_(1m) ofthe first QCM sensor 11 a and for the operation unit 14 to startcalculating the first change Δf_(1m) in the first oscillation frequencyf_(1m).

Moreover, a sixth time t_(g), which is the end of the third period T₃,is the time when the second change Δf_(2m) reaches a predeterminedspecified value F_(em). Also, the sixth time t_(g) is the time when theoperation unit 14 finishes acquiring the first oscillation frequencyf_(1m) and thus finishes calculating the first change Δf_(1m).

As described in the fifth embodiment, even though the first and secondQCM sensors 11 a and 11 b have the same specifications, the individualdifferences thereof causes a difference in slope between the first andsecond graphs A₁ and A₂ during the third period T₃.

To deal with this problem, in this embodiment, the following correctionis performed to match the slope of the second graph A₂ with the slope ofthe first graph A₁.

First, the operation unit 14 calculates a third ratio F_(g)/F_(em) ofthe first increment F_(g) of the first change Δf_(1m) within the thirdperiod T₃ to the second increment F_(em) of the second change Δf_(2m)within the third period 1 ₃, and sets the third ratio as a thirdcorrection coefficient C₃. The third correction coefficient C₃ thuscalculated is equal to a ratio between the slopes of the graphs A₁ andA₂ in FIG. 42 during the third period T₃.

After that, the operation unit 14 corrects the second change Δf_(2m) bymultiplying the second change Δf_(2m) at and after the sixth time t_(g)by the third correction coefficient C₃.

As already mentioned, the third correction coefficient C₃ is equal tothe ratio between the slopes of the graphs A₁ and A₂. Therefore, bycorrecting the second change Δf_(2m) in this manner, the slope of thesecond graph A₂ can be matched with the slope of the first graph A₁.

All examples and conditional language recited herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. An environmental measurement apparatuscomprising: an operation unit which calculates a first change in a firstoscillation frequency of a second QCM sensor, wherein the operation unitcorrects the second change based on the first change in a first periodand the second change in the first period, and wherein the operationunit obtains a first ratio of a first increment of the first changewithin the first period to a second increment of the second changewithin the first period, and corrects the second change by multiplyingthe second change by the first ratio.
 2. The environmental measurementapparatus according to claim 1, wherein the operation unit startsacquiring the second oscillation frequency at a first time within thefirst period, and finishes acquiring the first oscillation frequency ata second time within the first period.
 3. The environmental measurementapparatus according to claim 2, wherein the first QCM sensor includes: acrystal oscillator, a first electrode formed on one main surface of thecrystal oscillator, a second electrode formed on the other main surfaceof the crystal oscillator, where a voltage is to be applied between thesecond electrode and the first electrode, and a wire formed on at leastone of the one main surface and the other main surface, and theoperation unit sets as the first time a time when a resistance value ofthe wire exceeds a predetermined threshold.
 4. The environmentalmeasurement apparatus according to claim 2, wherein the operation unitcorrects the second change by adding the first change at the first timeto a value obtained by multiplying the second change by the first ratio.5. An environmental measurement method, the method comprising:calculating a first change in a first oscillation frequency of a firstQCM sensor; calculating a second change in a second oscillationfrequency of a second QCM sensor; correcting the second change based onthe first change in a first period and the second change in the firstperiod; and obtaining a first ratio of a first increment of the firstchange within the first period to a second increment of the secondchange within the first period, wherein the correcting the second changeincludes correcting the second change by multiplying the second changeby the first ratio.